This invention is directed to the improvement of brightness and contrast in monochrome and color cathode-ray tubes such as television picture tubes.
In the present state of the color television picture tube art, premium tubes for maximum brightness and optimum contrast are of the black-surround variety, in which the interleaved deposits of different phosphor materials are surrounded with a non-reflective or light-absorbing material which is usually colloidal graphite or some other black material. The provision of such a non-reflective grille surrounding the individual phosphor deposits reduces ambient light reflection from the front face of the picture tube in its operating environment and thus dramatically reduces contrast dilution from ambient light. This in turn permits the use of a clear glass or high-transmission filter faceplate which in turn transmits a greater amount of light generated at the phosphor screen and results in greatly enhanced picture brightness. Such a tube is described and claimed for example in U.S. Pat. No. 3,146,368 granted Aug. 25, 1964, to Joseph P. Fiore et al. and assigned to the same assignee as the present application.
Still further brightness increase and contrast improvement can be obtained as disclosed and claimed in the above-identified copending Dietch application, by providing a reflecting layer between the phosphor dots and the black-surround grille; this, together with the conventional metal backing layer, permits light generated behind the black-surround grille to find egress and contribute to picture brightness rather than being absorbed in the black-surround material.
To manufacture a color picture tube of the reverse-tolerance black-surround type shown and described in the above-identified Fiore et al patent, it is required that the grille of black-surround material be formed with interstices which are smaller than the holes of the associated shadow mask. Various processing techniques have been employed to achieve this objective, either by temporarily closing down the shadow mask apertures prior to photographic exposure of the screen forming resist or by initially forming the shadow mask with small apertures and later re-etching to enlarge the apertures after the black-surround grille and the phosphor screen have been formed. Such processing complications are obviously costly and difficult to practice on a mass-production basis.
It is a principal object of the present invention to provide a new and improved cathode-ray tube image screen.
A more particular object of the invention is to provide a new and improved image screen for a color cathode-ray tube which exhibits brightness/contrast performance comparable to or superior to even the best black-surround color television picture tubes.
A further and extremely important object of the invention is to provide such a new and improved cathode-ray tube image screen which can be manufactured without the use of complicated processing techniques such as temporary hole closure or re-etching of the shadow mask apertures.
Yet another object of the invention is to provide a new and improved image screen structure for cathode-ray tubes which is useful to provide greatly improved brightness/contrast performance from a monochrome or black-and-white cathode-ray tube.